Netgear HDX101 Homeplug
Nothing beats a good quality CAT5e or CAT6 network. Certainly not wireless and almost certainly not "homeplug" type devices.
Electrical cables were never meant to carry data.
Because I want to be sure I won't have fried network cards (or worse) in event of electrical storm if I run cables under ground between two separate buildings with different ground potential.
Personally, I would go with fibre and media converters. Also, I'm sure you know this, but don't use standard cable for external applications, get something with a tougher shell (sorry, the correct word escapes me at the moment !) ... either that or encase it in something... your own mini-duct.
Might not be as expensive as you may think. Just needs more care during install, and if self-installing, use pre-terminated fibre, don't try DIY fibre termination unless you've done it many times over and got the correct fusing/testing etc. kit.
Finally, if you are insistent on copper based cable between buildings, you might want to look at shielded cable.
But don't quote me on the legalities/safety .... I'm not a sparkie, and as I made clear above, for me, once something leaves a building it's pretty much fibre or nothing (unless someone else like BT is installing and taking the blame for a copper solution
)